In open pit mines, open pit quarries, and other types of open pit mining operations, blasting is carried out using vertical boreholes ranging in diameter from about 2 inches to about 17 inches. Blasting is carried out to remove overburden covering an ore body, and to break ore to allow it to be loaded and hauled away. Economic considerations require that blasting operations make optimum use of available explosive energy. This includes obtaining the desired breakage and throw of the ore. While accomplishing the above, it is becoming increasingly important to minimize the effects of blasting on nearby structures such as homes, schools and offices. To control rock fragmentation, rock throw and vibrations, it is often desirable to initiate a column of explosives at the bottom of a borehole. Such bottom hole initiation requires that the signal carrier, such as a detonator cord, which transmits the firing signal to the detonator in the bottom of the borehole not interact or react with the explosive column. This can be accomplished by either using a signal carrier which exerts no external force when it functions or by using an explosive column which is not effected by any action of the signal carrier when it functions.
When delay detonators are used in a blast to achieve bottom hole initiation, the number of boreholes which can be individually delayed to initiate at different times is limited by the available number of detonator delay periods or delay times. The use of a surface delay system in combination with an in-hole delay system could extend this number of individually delayed boreholes indefinitely.
In blasting, insensitive explosives or blasting agents such as ammonium nitrate-fuel oil compositions, for example, are detonated by booster or primer charges containing high explosives sensitive enough to be detonated by ordinary blasting caps. For safe and efficient use, the detonation of the primer charge that is used to initiate such blasting agents must be capable of being precisely timed and and must be highly reliable. While electric blasting caps have the advantage of precise timing, there are those who feel that the advantages of electrical ignition are outweighed by the potential for inadvertent energizing of all or part of the electric blasting circuit by extraneous electricity.
In using nonelectric detonators initiated by detonator cords, it is essential for reliable initiation that the detonator cord be adjacent that portion of the detonator that receives the explosive signal from the detonator cord. In addition, it is important that the detonator cord signal not directly interact with or initiate the primer explosive.
Therefore, a need exists for a nonelectric detonator for use in open pit mines and quarries where it is desired to achieve bottom hole initiation when used in conjunction with detonating cord. A need also exists for a simple, reliable, inexpensive and efficient device and method for securing a detonator cord in initiating relationship to a nonelectric detonator and for securing the nonelectric detonator to an explosive primer charge for initiation by the nonelectric detonator while protecting the primer charge from interaction or initiation by the detonator cord. In addition, a need exists for a device and method for a surface delay system that can be used in combination with an in-hole delay system for extending indefinitely the number of individually delayed boreholes.